Core sampling is typically employed to allow geological surveying of the ground for purposes of exploration and/or mine development. Analysis of the material within the core sample provides information of the composition of the ground. However in order to map, for example a vein of ore, it is necessary to also have knowledge of the orientation of the core sample relative to the ground from which it was cut.
Several systems are already known for orientating core samples. One such system is the BALLMARK (Trademark) system which is described in International Application No. WO 00/75480. This system utilises a soft metal disk and a free running metal ball which are incorporated into a conventional inner tube back end or head assembly. The system utilises the force generated during breaking a core from the parent rock strata to indent the soft metal disk with the metal ball. As the ball is free running, gravity causes it to be positioned at the lowest point in its track, which corresponds with the bottom side of the hole and consequently the bottom of the core.
The BALLMARK system has achieved high market acceptance and provides relatively high core orientation accuracy. Nevertheless, one drawback of the BALLMARK system is that it only operates by the actual breaking of the core. Core breaking involves lifting a drill string into which the core has advanced and applying sufficient tensile force to break the core from the bottom of the hole being drilled by the drill. However, in highly fractured or broken ground, the core breaks by itself during the drilling process. In this instance, the BALLMARK system will not operate.
A more rudimentary system for core marking involves running a marking tool, which in essence is in the form of a red pencil on the end of a counter balanced spear, by a wireline down the drill string to physically mark the core. A substantial drawback with this system is that it requires separate tripping of the tool down the hole which takes substantial time thereby reducing actual drilling time and substantially increasing the cost of coring.
Another marking system is the VAN RUTH wireline core orientator which utilises a plurality of slidable pins to provide a contour of the face of the core. Yet another system described in U.S. Pat. No. 4,311,201 relies on the use of a malleable material to provide an imprint of the face of the core. However, again both these systems require the separate tripping of a tool in order to provide orientation of the core.